Making of the SNX Hull

[Nate_D]

So a question for any machinist watching this thread...

What would cause stainless steel to eat through drill bits? I've drilled and tapped stainless many of times, and while it's a bitch to do, I've always been relatively successful without destroying too many tools in the process. However, today I was trying to drill some 3/16" 316 plate with a 1/4" drill bit. One of the holes made it through, the second hole ate 3 titanium HSS bits!

I kept a near constant stream of cutting fluid on the bit and plate. What would cause this? Could of dipping the hot SS plate piece in water after cutting it hardened the plate? Seems ridiculous. I gave up after the third bit and made the jig from 6061.


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[///M5]

You need cobalt or better to make it easier

 

[makejetskiinggreatagain]

What RPM's were you using to drill? for a 1/4" HSS drill going through 316 I would use roughly 700-1000 rpms. If you don't know exactly how fast you are going then remember that spinning slower than recommended is way better than spinning faster than recommended. If you were using a hand drill you should start really slow and speed it up until the drill just starts cutting then stay at that speed. always add cutting fluid like you mentioned you did. You may have spun the drill too fast and burnt it up. When you did that, you probably also work hardened the material so you set yourself up for the next drill to burn up right away trying to drill through even harder material. Also, when I use a HSS drill I always use a spot drill first. Otherwise that HSS drill will be a bastard to get to start cutting because it will have the tendency to walk all over the place. at 1/4" They are just too flexible to use without a spot drill. If you dont have a spot drill You could limp through by choking way up on the drill (not recommended) so that only about 3/8" is sticking out. then it will be rigid enough to start your hole. Then once its started, clamp on the drill behind the flutes and go to town slowly.

 

[Nate_D]

Thanks for the advice M5 and WD! I was set at 700. I used a punch to mark the hole and keep the bit from walking. The cheapo HF press I'm using has a lot of runout in the spindle though, so getting a clean hole into anything is a challenge at times. I think you are correct about the work hardening.

It's been one of those days where everything takes far longer than it should and nothing gets accomplished. In 5 hours I think I managed to make one jig that had 6 holes in it, and cut another 8 holes into one of the poles. I hate working with metal.


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[jetskipunk]

Yes. Slow the rpm and increase feed for stainless. It can be done w HSS, but speed/feed must be dead on. Cobalt is a better option tho. Another option (for sheet) might be to plunge a carbide endmill.

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[txsuperjetfreak96]

I got one of those cheap hf drill presses was shockec at how much play the spindle has


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[speedysprocket]

I always start with drilling a small pilot hole and keep increases drill bit sizes till I get to the size I want. Would 304 stainless be softer for next time...?

 

[txsuperjetfreak96]

I agree on pilot holes and going bigger even though im in patient. Sometimes metal can b harder in one spot and not as hard in another


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[302much]

304 and 316 wont harden from heat treatment, but will harden from cold working. you should be able to pull very long chips off of the bit as an indication you are cutting at the right speed/pressure. you may be able to anneal it (heat to 1900, quench in water) to soften the hardened area if you don't have another piece.

I read through this entire thread about a week ago, took me like two hours... You have done some very impressive work.

 

[makejetskiinggreatagain]

why wouldnt a 300 series stainless work harden? Not disagreeing just curious. I dont run much of it. I run mostly hardened 17-4, 455, and 465.

edit: a quick google search found a bunch of threads about 316 work hardening....they could be started by hobby machinists with very little experience, but i cant find anything about 316 not being able to work harden.

 

[302much]

work hardening can be achieved through heat or grain distortion (yielding). the temperature wont effect 300 series stainless. either way it comes down to speed/feed rate to prevent it fom becoming excessively hard. you can see the small chips in the photos he posted, they are an indication that it wasn't cutting correctly.

Also, 304 and 316 are essential the same, 304 being slightly harder, but 316 has better corrosion resistance.

 

[Nate_D]

304 and 316 wont harden from heat treatment, but will harden from cold working. you should be able to pull very long chips off of the bit as an indication you are cutting at the right speed/pressure. you may be able to anneal it (heat to 1900, quench in water) to soften the hardened area if you don't have another piece.

I read through this entire thread about a week ago, took me like two hours... You have done some very impressive work.

Thanks for the compliment! I always like to hear that other people appreciate the work I am doing.

I've got several piece of miscellaneous stainless and 6061 plate laying around. The whole reason I even used the 316 was because it is easier to cut with a cut off wheel than the aluminum. I tossed the piece and used the aluminum instead.

It's sad, but this is what I spent the better part of 5 hours making...

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[302much]

Ouch! you probably could have made it from carbon fiber a lot faster lol

 

[makejetskiinggreatagain]

work hardening can be achieved through heat or grain distortion (yielding). the temperature wont effect 300 series stainless. either way it comes down to speed/feed rate to prevent it fom becoming excessively hard. you can see the small chips in the photos he posted, they are an indication that it wasn't cutting correctly.

Also, 304 and 316 are essential the same, 304 being slightly harder, but 316 has better corrosion resistance.

This site says 316 cant be hardened by thermal treatment but can be easily work hardened. Not being argumentative i just didnt know what the right answer to the work hardening question was. for others who are curious here is the link to 316 properties
http://www.azom.com/article.aspx?ArticleID=2382

 

[302much]

right, i guess what I'm trying to say is that because it doesn't harden from heat you could still harden the metal/ruin drill bits etc.. even if the part was immersed in cutting fluid.

 

[makejetskiinggreatagain]

i wasnt trying to be argumentative, just trying to learn from people who may have more experience than me

 

[SirMrManGuy]

Thanks for the compliment! I always like to hear that other people appreciate the work I am doing.

I've got several piece of miscellaneous stainless and 6061 plate laying around. The whole reason I even used the 316 was because it is easier to cut with a cut off wheel than the aluminum. I tossed the piece and used the aluminum instead.

It's sad, but this is what I spent the better part of 5 hours making...
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The aluminum you should be able to cut with a decent jig saw and/or circular saw and a ton of wd40.

There are also a few guys on here with machine shops that would probably do some deals on making those plates for you if you wanted stainless. Those parts are a gravy job on a decent VMC. If I had my shop setup, and wasn't half way around the world I'd be all over knocking out a bunch in exchange for a pole.

 

[cookn]

If you burn a drill bit in the hole it gets work hardened as well making it harder for the next drill to get through it

 

[Mark44]

use a pilot hole slow speeds and some cutting fluid. (oil)

 

[Nate_D]

Thanks for all of the advice guys! Like I mentioned before, metalworking is not a strong skill set for me. Looks like it was a combination of feed rate, a dull bit, and work hardening. Learned something new.


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